The purpose of this study is to identify the existence and extent of biases associated with HMO full electronic and claims-type encounter data when they are used to characterize patterns of care and to analyze the relationship between treatment and outcomes of breast and cervical cancers. Electronic data assessed will include inpatient and outpatient visits, pharmacy, cancer registry, pathology, radiology, laboratory, and electronic physician notes. This project is a joint venture between four not-for-profit HMOs: Fallon/Meyers Primary Care Institute, Kaiser Permanente/Northern California, Health Partners Research Foundation and Henry Ford Health System. A patient who was diagnosed for breast cancer between January 1, 1996 and December 31, 1997 or for cervical cancer between January 1, 1996 and December 31, 2000 will be included in the study. A study central database will be established to contain all electronic and claims-type encounter data on medical care of these patients. Medical record information will be abstracted for a random sample of 925 breast cancer and 995 cervical cancer patients. The study will compare information in the electronic data sources to information abstracted from medical records, and assess differences in completeness and accuracy of diagnostic, treatment, and outcomes by patient characteristics, among HMOs, and by source of data. Using data abstracted from medical record and electronic data, we will characterize the patterns of care and assess the relationship between treatment and outcomes among women of any age with cervical cancer and women age 55 or older with breast cancer. This study will provide important information about the feasibility of using computerized claims data as well as other computerized resources for the study of cancer treatment and outcomes. The primary strength of the study is that it uses routinely and efficiently collected population based electronic data to identify cancer patients, treatments and outcomes. If these databases are shown to be valid, they provide promising resources for cancer studies, with extensive information on treatment, follow-up and outcome far exceeding those available from traditional cancer registries.